1. Field of the Invention
The present invention relates to teleprinters for automatically printing alphanumeric characters.
2. Description of the Prior Art
Teleprinters are known which facilitate both the setting up of texts composed of characters in local operation and also the remote transmission of these texts. Such teleprinters generally consist of at least one input unit, a central control unit, a line-matching unit which establishes the connection of the teleprinter to a trunk line, and at least one output unit and a current supply unit. The input unit generally consists of a keyboard or a punched strip reader whereas the output units generally consist of a printer and a punched strip puncher. In more recent teleprinters, a display unit which may be, for example, a cathode ray tube is additionally provided by way of output unit. A floppy disk store is also provided which can be used both as an input unit and as an output unit and which is capable of replacing punched strip devices.
For transmission purposes the teleprinter characters are coded in accordance with international telegraph alphabet No. 2 and are provided with start- and stop- elements. The synchronization between the transmitting and receiving teleprinters is effected in that each transmitted character serves to re-start the printer in the receiving teleprinter. The printer remains in the column of the last character to have been printed or in the next column and waits for the reception of the next character. This applies particularly when characters are input by means of the keyboard at a low input speed.
The start-stop operation imposes considerable demands on the units which operate character-by-character, in particular on the printer. During the time between two received characters the printer must accelerate and then deccelerate at the print-out position. In the case of type printing, for example using a type-wheel, the printer must be brought to a halt even before print-out. Following the print-out of the last character it is also frequently necessary to position the printer in such manner that having been printed the last character can be read by the operator. Finally it is also necessary to carry out a carriage return step and a character feed step, i.e. to bring the printer from the end of the row into the starting position of the next row during the time between two received characters.
In this mode of operation which is common in teleprinters, for a short period of time and a very large amount of energy is required to move the printer and the mains component of the teleprinter must possess high power reserves for this mode of operation. In addition large motors are needed in order to be able to carry out the movements of the printer at sufficient speed. Finally very considerable requirements exist in respect of mechanical accuracy. The overall consequence is that teleprinters designed for start-stop operation necessitate a relatively large outlay and the production costs are correspondingly high.